The present invention is directed to aspiration-type sprayers for use in dispensing small quantities of a liquid- based chemical into a relatively large quantity of a carrier fluid. The device is particularly suited for lawn and garden and agricultural applications where chemicals, such as pesticides and fertilizers are applied to crops, plants, lawns and other vegetation. Because of the usually hazardous nature of the chemicals to be applied, it is desirable to market such products in containers which are permanently sealed to a sprayer head so as to minimize inadvertent human exposure, such as from careless handling or unauthorized access by children, to a concentrated chemical. To make such nonrefillable products economically feasible it is necessary to provide a sprayer which is of sufficiently low cost to allow the entire unit to be discarded when the container contents have been exhausted. It is therefore desirable to provide a sprayer which is inexpensive to manufacture and yet will reliably and safely provide a wide range of mixing ratios to meet the particular requirements of the individual user.
Prior art sprayers, such as that shown in Chow et al. U.S. Pat. No. 4,750,674, the disclosure of which is hereby incorporated by reference, teaches a sprayer assembly having a system of air vent and aspiration openings of different sizes to obtain a selection of discrete mixing ratios. The mechanism requires a system of cups to block openings associated with nonselected aspiration rates and to provide the desired fluid communication. Such a system, however, requires the alignment and assembly of a plurality of elements including openings, cup seals and springs. Such a system complicates manufacture and assembly thereby failing to fully minimize cost. Further, such devices fail to provide a simplified sprayer with a minimum of complex moving parts and a continuous range of mixing ratios. Employing the teaching of Chow et al., a range of mixing ratios would require a prohibitively complicated system of moving cup seals for alignment with a large number of alternative sized aspiration openings.
Other prior art sprayers, such as that shown in George et al. U.S. Pat. No. 3,186,643, the disclosure of which is hereby incorporated by reference, use a rotating carrier fluid valve having a range of adjustability of carrier fluid flow in combination with a vent bore closure boss extending from the rotating valve. Such control of carrier fluid flow fails to provide means for varying the desired rate of chemical dispensing while maintaining a selected distance and strength of spray projection.
Therefore a need exists for an aspiration-type chemical sprayer having simplified design and ease of manufacture which provides a range of direct control of the aspiration passageway while providing for leak resistant operation and secure and simultaneous closure of both the aspiration and vent passageways for positive chemical flow shut-off when the sprayer is not in use.